ESSAY ON CLASSIFICATION 



CHAPTER I 



THE FUNDAMENTAL RELATIONS OF ANIMALS ONE TO 

 ANOTHER AND TO THE WORLD IN WHICH THEY LIVE 

 AS THE BASIS OF THE NATURAL SYSTEM OF ANIMALS 



SECTION I 



THE LEADING FEATURES OF A NATURAL ZOOLOGICAL SYSTEM 

 ARE ALL FOUNDED IN NATURE 



Modern classifications of animals and plants are based upon the 

 peculiarities of their structure; and this is generally considered as 

 the most important, if not the only safe, guide in our attempts to 

 determine the natural relations which exist between animals. This 

 view of the subject seems to me, however, to circumscribe the founda- 

 tion of a natural system of Zoology and Botany within too narrow 

 liinits, to exclude from our consideration some of the most striking 

 characteristics of the two organic kingdoms of nature, and to leave 

 it doubtful how far the arrangement thus obtained is founded in 

 reality, and how far it is merely the expression of our estimate of 

 these structural differences. It has appeared to me appropriate there- 

 fore to present here a short exposition of the leading features of the 

 animal kingdom, as an introduction to the study of Natural History 

 in general and of Embryology in particular, as it would afford a 

 desirable opportunity of establishing a standard of comparison be- 

 tween the changes animals undergo during their growth, and the 

 permanent characters of full-grown individuals of other types, and 

 perhaps of showing also what other points beside structure might 

 with advantage be considered in ascertaining the manifold relations 



